Method of artificially seasoning lumber



Sept. 22, 1942. `w ToNEY METHOD OF ARTIFICIALLY SEASONING LUMBER 3 Sheets-Sheet 1 Filed March l5, 1941 Sept. 22, l1942. w. ToNEY METHOD OF ARTIFICIALLY SEASONING LUMBER 3 Sheets-Sheet 2 Filed March l5, 1941 W. TONEY sept. 2v2, 1942.

METHOD OF ARTIFICIALLY SEASONING LUMBER Filed March l5, 1941 for sawed stock while Patented Sept. 22, 1942 2,296,546 Ms'rnon or ABTIFI'CIALLY sEAsoNING ummm wilma remy, crossen, Ark., assigner to crossen Lumber Company, A of Arkansas l Application Crosse, Ark.,

a corporation Maren 15, 1941, sensi No. 363,633

' 1o melma (01.34-15) This invention relates to the seasoning of lumber as it is produced at the sawmill to dry it and prepare it for shipment and use, and particularly to a method involving the use of steam under low pressure in a suitable vacuum chamber.

Air drying lumber out of doors cannot be satisfactorily practiced at all seasons of the year, and it may take from six weeks to eight or more months to air dry one inch common pine lumber, depending upon the time'of year and weather conditions, in order to obtain results within the requirements vfor moisture content and uniformity. Thus the problem of storage and protection drying by air is a serious one; and the same applies to kiln dried lumber to a substantial degree, which, according to pre'- vailing methods, requires from sixty to ninety hours, and results in an objectionable degrading andvwastage of the stock thus treated.

My invention aims to reduce the time heretofore found necessary for seasoning'lumber by air or in dry-kilns, and to improve the uniformity and quality of the product without increasing the wastage and degrading attendant upon present methods. The invention further aims to reduce the cost of kiln-drying lumber by utilizing I the energy of the live ing and circulating steam used for both heatthe vapors produced in the vtreating of lumber, and preventing waste of heat.

The invention comprises first lumber with steam at low pressure and in a partial vacuum to soften the wood and remove`objectionable constituents of the sap, followed by kiln-drying the partially dehydrated lumber while hot under controlled humidity and temperature conditions to reduce the 'moisture content to the desired amount, all as one continuous process.

Further details and advantages of the invention appear in connection with the following description and the accompanying illustrative examples, and what, the invention comprises more fully appears in the appended claims.

The invention may be 'practiced with the aid of large pressure cylinders, steam control valves, pumps, humidity control apparatus etc. now available in the industry, together with dry kilns of either the compartment or continuous type, and noclaim is made herein for the apparatus as such although the combination of facilities and instruments for carrying out the process is believed to be new in the art of seasoning lumber.

treating the` such as a steel cylinder II y heating coils I6 facing towards For illustrative purposes, the invention is herel in described in connection with the apparatus disclosed in the accompanying drawings, wherein Fig. 1 is a longitudinal section taken vertically on the principal axis of a pressure and vacuum treating cylinder large enough to receive a truckload of lumber; Fig. 2 is a vertical cross section thereof on the line 2-2 in Fig. 1; Fig. 3 is a vertical longitudinal cross section of a drying kiln, drawn to approximately the saine scale as Figs. 1 and 2, the vsection being taken on the line 3--3 -in Fig. 4; Fig. 4 is a vertical cross section of the dry kiln on the line 4--4 in Fig. 3 looking in the direction of the arrows; and Fig. 5 is a vertical cross section of the dry kiln ou the line l--I in Fig. 3, looking in the opposite direction to that ofthe arrows and drawn to a smaller scale.

The process may be conveniently divided into two parts, the first part being conducted preferably in a large steam heated pressure chamber,

of ample size to receive a. car of lumber I2 and having doors I3 at one or both ends capable .of withstanding steam pressure up to ve or ten pounds and a vacuurn of from fourteen to twenty inches or more of mercury, which may be heated with steam coils I4. This cylinder is provided with a supply of steam through a valve I5 at a slight degree of superheat, said steam being discharged into the pressurechamber through openings in the side the lumber. Bottom cooling -coiis I1 are provided, through which cold water may be circulated from" a valved supply pipe I8, and discharged through a surface condenser I9, the shell of which is connected to the cylinder by a valved pipe 20 and to a vacuum pump 2l discharging into the atmosphere.

' a vacuum of fourteen inches or so. The second part oi the process may be conducted advantageously in a drying kiln 30 having steam heating coils 3l and spray pipes 32, circulating fans 33, baiiles 3l and Ventilating ilues 35, and automatic humiditiy controlling and the drying kilns and pressure cylinders are preierably arranged for rapid and convenient, transferring of the successive lumber charges from one to the other with as little delay and loss of heat from the lumber as possible.

In carrying out the process,

A valved bleeder pipe 22 and trap 23 for condensate a charge of lum-v 2 acoaue ber, stacked to provide a plurality of vertical Charge No. 1, material-1" #2 Com.

circulating dues, is run into the pressure cylinder, the doors are closed, and live steam at from Time sm three to live pounds pressure turned into the Pressure or Temperechamber, the steam being distributed throughout 5 stm End "mum tu coils Liv Y steam the chamber from two or more side pipes IG provided with ne oriilces to discharge the steam at i high velocity and promote circulation through :gigs gglaul--- the charge. Steam is also admitted to the heatibo 1:45 me 'e'i ingcoils l5 to bring them up to a temperature oi' '10 gig gglilf" 220 to 230 F. The steam is left on for from 3545 45m Held av'III-- two to four and one-haii hours, being turned oil when the lumber is heated throughout to a tem` uso nem-u cylinder cime. perature of about 220 F.. which may be 'ascer- 90mm@ 0m yundl`d tained by periodically reading the temperature within the cylinder and stopping the processA 'rime in Kglg'y we: bulb ,xlgfi" when lthe temperature et the middle or the stack f "S- temperature www 'ny ceases to rise, indicating that a balance has been reached between absorption of heat by the lumy Perm: ber and vaporization of its most readily vapor- 2o 205 i?? ized constituents at the pressure at which the e 21o 175 4e steam is supplied, which is not; high enough to 6 m "o u injure the wood.

The pressure: cylinder is equipped with a gsmknryuignseime, bleeder pipe 22 and trap 23, and a bottom vent 25 Average I noistum 16%. 2 4, to permit draining of condensate and sap ex- Rmks N mps'cnechwwm' pelled from the wood by the steam and heat, all Charge No. 2, material-1" #2 Com. during the heating operation.y and this vent 24 is i opened full at the completion oi the heating to Time Y steam permit the surplus steam to blow oi rapidly, pre- Pressure or Tempera- A peretory te ciosingui'e vent and exhausting the am, d "cum um com Live remaining vapor by means of the vacuum pump. am A top blow-oi valve 25 is also provided to expe- 9m 1200 222 on on dite the operation. The cooling coil circulating i ,21m 11m 222 onjjjj on water is turned .on throughout the steam and 83:-- gg vacuum treatment to promote circulation and 2315 3515 182 Ong: 0 assist in reducing the pressure rapidly after the 3115 3=45 162 011 Off blow oiT valve is closed. The vacuum treatment om] und, um is continued at about 14 inches of mercury, so mcy e' long as vapor continues to be given o by the 40 Cwdmm "um Wunde' .O'K' wood, usually for about two' and one-half hours. i steam being left in the heating cous during this 'Pme TL mige Ru'fii." operation, at th'e end of which time the tempera- 9mm "Y ture will have dropped to about 160 F. and the y vacuum may be about 20 inches ot mercury, this 45 2 ma f 180 Pe'gm being some six or eight degrees higher than the c m5 17s 54 boiling point of the saturated vapor at the low 2 13 gg E pressure maintained/by the vacuum pump. Live steam is admitted to' the cylinder periodically 18 Oumma during the vacuum treating operation to pro- 24.7wta1dryinetime. mote circulation vand add heat to the contents um mmm mm. 14%' of th'e'cylinder, thereby preventing condensation Charge No- 3 'numb-'1 #2 Comoi moisture fromremaining on the lumber and also preventing surface checking of the wood due Tim@ Steam l to the temperature in the cylinder being hotter PIM@ 0r litllllirwrthan that of the lum This treatment is iol- Suu-e nud vacuum e oeils am lowed by opening the cylinder and transfeil'irg the lumber charge to the dry kilns with as e less erneut as possible. 11.53 531%? Eiw 22g 83 33 l By'thls method of treatment, a substantial part 60 ggg lgg 310215,? g: 8g f the original mOlStllre in the gteen'wOOdl i8 VE.- 115 2215 i Bgld 14" 152 0n 0n porized in the vacuum cylinder and carried away 215 2F45 Held 20 162 011 01* without aecting the resinous constituents or y injuring the surface or interior of the wood: and 7-08 hom @Undef timethe lumber is put in condition for rapid treatment in the dry kiln, whereby closely controlling 'rime in 21h23 Wei bulb 112mg? the heat and the humidity and main I 1 Y 1 i hmm pei-ame empeatm/'e ity rapid and thorough circulation of the atmosphere and removal o'f moisture therefrom,from l Per een: eighteen to twenty-four hours treatment suces 93g i?? 2 to reduce the moisture content of the wood to e 21o 115 `is the degree desired for marketing the lumber. 6 21 17 42 The following examples are typical of the prowho kun um cedure as applied to 1 inch and 2 inch common www dmim9 southern pine lumber fresh from th'e saw: 75 Average moisture wur/eut 16%,

Charge No. 4, material-2" #1 Com.

Time Steam Pressure or Temperavacuum ure Live Start Bind Coils steam 4:45 7:45 Up to 5# 228 On 0n 7:45 9:15 Held 5# 228 0n 0n 9:15 9:30 Blowing oil 0n 0H 9:30 10130 Up to 14 182 On Oil 10:30 11:30 Held 14 182 0n On 11:30 12:00 Held 20 162 O11l O 7.25 hours cylinder time. Condition from cylinder, good.

Kiln dry l Relative Time in Wet bulb hours bpuelrg' temperature huiltnyid' Per cent 6 200 180 68 205 175 54 6 210 175 46 6 210 170 42 Lf 24 hours kiln time.

31.25 total drying time.

From the foregoing examples of the treatment as applied to common pine lumber, it will be noted that the green lumber is subjected in the steam heated pressure cylinder to the action of substantially dry live steam at from 3 to 5 lbs. pressure for a period of from three and one-half throughout to a temperature of 220 F. or thereabouts without injury, followed by blowing off the steam and carrying with it the condensate and part of the readily Vaporizable constituents wise injuring the wood so as to prevent its being finished without cupping, warping, splitting or otherwise failing to meet the requirements of manufacturers and users of properly seasoned lumber. The high temperatures and short time cient to heat and soften the wood followed .by

' reducing the pressure to vaporize internal conand surfacemoisture to partially dry the same,

vto four and one-half hours, sufilcient to' heat it The lumber is transferred to the dry kiln at its temperature of 160 F. or thereabouts, and gradually raised ,to about 200 F. by thesteam coils and steam and air circulated therein, the humidity being controlled between 68% and 42%, in the successive stages by the admission 1 of steam and air and withdrawal of vapor during the drying process and resulting in the removal of about more of the original moisture, leaving some 14% to 16% in the wood, which is satisfactory for shipping and marketing it, the entire operation taking place in from 24 to 32 hours, as compared with from 60 to 90 hours to dry the same lumber to the same moisture content by the usual dry kiln processes not involving preliminary live steam and. vacuum treatment.

The temperature and duration of the treatment in the dry kilns are regulated and timed in each of the four stages or compartments to suit the condition of the wood, as determined by tests of its moisture content, the aim being to expel about 32% in the iirst stage, about 15% in the second stage, about 8% in the third stage, and about 4% in the last stage, without case hardening the wood or causing internal or superiicial checks or cracks, loosening knots, or otherstituents of the wood at a higher temperature than that corresponding to the steam at the reduced pressure, the temperature ranging from above to below that of boiling water at atmospheric pressure, until at least 20% o! the vaporizable constituents have been expelled, re-

moving the Vaporizedconstituents of the wood and subjecting the heated charge to combined heat and moisture in a circulating atmosphere of controlled humidity and temperature in successive stages o! decreasing humidity and increasing temperature for periods oi time sumcient tovaporize successive decreasing increments of internal moisture whereby substantially 60% more of the originally vaporizable constituents of the charge are vaporized and expelled, the entire series of treatments being carried out as a continuousA process and completed in not more than 30 hours forjlumber not over one inchin thickness.

2. The process of claim 1 wherein the first heating bylive steam does not exceed a temperature of about 225 F.

3. The process of claim 1 wherein the reduction in pressure following the heating by live steam is of the order of about one-half an atmosphere.

4. The process of claim 1 wherein the steam heating and reduced pressure vapor-ization treatments do not exceed eight hours in time.

5. The process .of claim 1 wherein the successive treatments at decreasing humidity and increasing temperature, de not exceed the equivsive stages each bears approximately a constant ratio to preceding and succeeding increments.

d. The method of seasoning sawed lumber containing sap which comprises stacking in charges of similar sizes and subjecting each charge to live steam under low pressure insuiiicient to remove the resinous constituents and change the character o the wood for a length of time sumcient to heat and soften the wood and dilute the moisture contained in the sap, followed by reducing the pressure to vaporize said diluted sap moisture, the temperature varying from not over twenty degrees above during the pressure treatment to about thirty degrees below during the and vacuum treatment whichA the charge, subjecting the heated chargeto combined heat and moisture in a circulating-atmosphere oi' controlled humidity and temperature insuccessive stages of decreasing humidity and increasing temperature for periods of time sumcient to vaporlze successive decreasing increments ot internal moisture whereby sixty per cent more of the originally vaporizable constituents of the charge` are vaporized and expelled, the entire series ot treatments being carried out las a continuous process.' substantially as 5 described.

9. The process of claim 8 wherein live steaml is introduced during the reduced pressure stage.

10. The process of claim 8 wherein the circulating atmosphere comprises live steamv and air 10 commingled to assist in the circulation thereof through the charge.

ToNEY. 

